Apparatus for developing a latent charged image

ABSTRACT

An apparatus for uniformly developing a latent charged image carried on electrophotographic paper by moving the electrophotographic paper past a support surface with the reverse side of the electrophotographic paper contacting the support surface, and rotating a conductive roller partially immersed in a liquid toner bath, the conductive roller having an electrical potential supplied thereto and having a peripheral surface spaced from the image side of the paper supported on the support surface. The support surface includes a conductive area and a non-conductive insulating area which are selectively engaged against the reverse side of the paper for direct development and reverse development, respectively.

United States Patent Deshayes et al.

APPARATUS FOR DEVELOPING A LATENT CHARGED IMAGE Inventors: Phillippe M. Deshayes, Neuville Les Dieppe; Guy Paul Weber, Arques La Bataille, both of France Related US. Application Data Continuation-impart of Ser. No. 277,059, Aug. 1, 1972. v

Foreign Application Priority Data Aug. 2, 1972 France 72.27802 US. Cl. 118/637; 117/37 LE; 118/DIG. 23 Int. Cl G03G 13/00 Field of Search 118/637, DIG. 23;

117/37 LE, 93.4 A

References Cited UNITED STATES PATENTS 10/1958 Pritchard l18/DIG. 23 4/1963 Gundlach l18/D1G. 23

[ June 3, 1975 Primary ExaminerMervin Stein Assistant Examinerl .eo Millstein Attorney, Agent, or Firm-Sherman & Shalloway ABSTRACT An apparatus for uniformly developing a latent charged image carried on electrophotographic paper by moving the electrophotographic paper past a support surface with the reverse side of the electrophotographic paper contacting the support surface, and rotating a conductive roller partially immersed in a liquid toner bath, the conductive roller having an electrical potential supplied thereto and having a peripheral surface spaced from the image side of the paper supported on the support surface. The support surface includes a conductive area and a non-conductive insulating area which are selectively engaged against the reverse side of the paper for direct development and reverse development, respectively.

7 Claims, 2 Drawing Figures ENTER JUH 3 ms SHEET PATENTEDJUM 1915 3886300 SHEET 2 APPARATUS FOR DEVELOPING A LATENT CHARGED IMAGE This application is a continuation-in-part of our copending US. application Ser. No. 277,059, filed Aug. 1, 1972f BACKGROUND OF THE INVENTION The present invention pertains to electrophotographic reproduction and, more particularly, to an ap- DISCUSSION OF THE PRIOR ART Our above-mentioned application sets forth a method and apparatus which exceeds the prior art by developing electrophotographic or electrosensitive bases or papers in a liquid within a controlled-potential zone or field. v

The paper carrying the charge-image is passed through the developing zone with its backing in contact with a member which is regulated to a selected potential, while the sensitive or face layer is adjacent but spaced from an opposite second member which is regulated to a selected potential.

The developer liquid is presented to the sensitive face in and adjacent the carefully maintained clearance between the sensitive face and the second member of regulated potential.

The apparatus of our earlier application includes a driven roller of controlled potential which is in contact with a bath of developer and which carries a film of developer around to the sensitive face of the paper. The back'of the paper is supported by a backing member of regulated potential and thereby is positioned closely adjacent but spaced from the surface of the roller.

The developer liquid carried by the surface of the roller then forms a small pool or meniscus in and adjacent the close clearance between the sensitive face of the paper and the roller.

The method and apparatus of our earlier application have proven themselves to be particularly effective and advantageous, particularly with regard to the prior problems of edge effect encountered because of nonuniform charge distribution in prior art systems.

When a positive image is to be made, the potential of the roller and the particles of the developer are at a potential or charge opposite in polarity to the charge of the latent charge image of the sensitive face of the paper to produce a direct development.

When reverse development or negative reproduction is desired, the particles of the developer are at a charge similar in polarity to the charge of the latent charge image.

The regulation of the polarity and intensity of the field, which is maintained at the zone of the junction of the developer meniscus, must be reasonably closely controlled.

In the case of reverse development, however, the accuracy of control of the field can become quite critical. If the proper charges in the field are not held to the requisite range of potentials, trace deposits of developer particles may occur in the area of the latent charge image. This causes random darkening of the image areas which should be light, thereby detracting from the quality of the reproduction.

Our present invention provides a solution to the problem occasionally encountered in our prior system.

SUMMARY OF THE INVENTION The preferred apparatus of the present invention is generally characterized in an apparatus for uniformly developing a latent charged image carried on electrophotographic paper or other base which includes passing the electrophotographic paper over a field member with the reverse or back of the paper in contact with the field member, positioning a conductive roller such that'the perephery thereof is close to but spaced from the sensitive face of the paper, the conductive roller having an electrical potential applied thereto, and rotating the conductive roller at least partially immersed in a liquid developer or toner bath at a speed sufficient to draw a thin layer of liquid toner along the peripheral surface of the roller and to form a kinetic pool or meniscus of liquid toner at the sensitive surface of the electrophotographic paper.

In general, the preferred form of apparatus of the present invention is characterized by a developing unit including a support surface, a conductive roller adjacent and spaced from said support surface, a reservoir for containing a bath of liquid toner in contact with said conductive roller, transport means for transporting paper between said support surface and said roller with the back side of the paper in contact with the support surface while the sensitive face of the paper is spaced from the roller, drive means for driving said roller, field means for establishing a selected field of potentials between said support surface and said roller, said support surface including a conductive surface and a nonconducting surface, and means for optionally presenting one of said conducting and non-conducting surfaces for engagement with said paper.

OBJECTS OF THE INVENTION It is. an object of the present invention to provide an apparatus for uniform development of latent charged images in direct or reverse development.

Another object of the invention is to provide a method of reverse developing electrophotographic latent charged images in a liquid developer medium to eliminate random spotting of the image areas.

A further object of the invention is to provide a method for direct developing or reverse developing of latent charged images in a potential field and without the necessity for critical precision in the regulation of the potential of the field.

Another object of the invention is the provision of apparatus for the direct or reverse development of latent charge images in a field between field members which are capable of being charged at different polarities, and the provision of one of the field members with conductive and non-conductive surfaces which are selectively employable in the potential field.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention as well as a better understanding thereof may be derived from the following description and accompanying drawings, in which:

FIG. 1 is a schematic, sectional view of electrophotographic paper having latent charge images thereon and showing apparatus and lines of force and charges presented to the electrophotographic paper and images in reverse development of the latent charge images, and

FIG. 2 is a diagrammatic view of an electrophotographic reproduction system embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, which presents the preferred method of reverse development of images, an electrophotographic base of paper 1, or the like, comprising a backing 2 and a sensitive face 3 bears against the surface 4 of a field member 5. The field member 5, for reverse development, is formed of a non-conducting or insulating material.

Opposite and spaced from the sensitive face 3 of the paper, a surface 6 of a conducting field member 7 carried a film or meniscus of developer or toner 8. The toner 8 includes particles 9 which are represented as plus signs within a circle.

The sensitive face 3 of the paper has latent charge images 10 thereon, which are represented by plus signs drawn in heavy lines.

The presence of the positive latent charge images 10 induces a balancing negative charge, represented by lighter minus signs 1 1, on the opposite side or back 2 of the paper. In turn, the negative charges 11 provoke compensating positive charges, represented by lighter plus signs 12, on the surface 4 of the insulating field member 5.

The surface 4 then exhibits negatively charged areas 13 intermediate the areas of the latent charge images 10. The negatively charged areas 13 of the insulating surface 4 correspondingly establish positive charge areas 14 on the adjacent area of the backing 2 of the paper which, in turn, creates corresponding negative charge areas 15 on the sensitive surface 3, in the intervals between the latent images 10.

Therefore, with the conducting field member grounded, the positively-charged particles 9 are repelled by the positive latent images 10 and are attracted to the intermediate areas 15 which have an induced negative charge thereon as a result of the presence of the insulating field member 5.

It is to be understood that, although positive-charge toner particles 9 and positive image charges 10 have been shown, it is possible to effect the reverse development regardless of the actual charge, as long as the image charge and the toner charge are of the same polarity.

If desired, the reverse development may be further regulated by supplying a positive potential to the conducting field member 7. However, this charging of the field member 7 again must be carefully controlled, particularly where relatively thin images of low potential are encountered, such as with half-tone images.

The preferred form of apparatus of the invention is shown in FIG. 2, in which a strip of electrophotographic paper 21 having a latent charge image on its sensitive face 23 is driven by rollers 24 and 25 to contact the support surface a field member 26 with the backing 22 thereof bearing solidly against the field member.

A roller 27 of conductive material is mounted with its periphery adjacent but uniformly spaced from the sensitive face 23.

The conductive roller 27 is driven by a variable speed drive (not shown) and preferably includes a textured or knurled outer surface, all in accordance with the teaching of our aforementioned US. application Ser. No. 277,059, filed Aug. 1, 1972.

In its lower region, the conductive roller 27 is partially immersed in a bath of developer or toner 28 within a reservoir 29, so that a film ofthe toner is drawn with the surface of the roller and forms a dynamic pool or meniscus 30 in and adjacent the clearance between the sensitive face 23 of the paper and the surface of the roll 27.

The strip of paper 21 is tensioned and advanced by pairs of transport rollers 31,32 and 33,34, respectively. The tension imposed by the rollers 31,32 must be sufficient to preclude any sag in the sheet 21 and any contact of the paper sheet 21 with the surface of the roller 27.

The rollers 31 and 32 are associated with drying means including a collecting receiver 35 for excess toner and a wiping blade 36 of felt or similar material.

Intermediate the drying section and the rolls 33,34, the system includes a cutting mechanism 37.

The field member 26 includes two halves 38 and 39 having contiguous arcuate surfaces 41 and 42. It is mounted on an axle 40 which permits the arcuate outer surfaces 41 and 42 to move to alternately bear against the back 22 of the paper 21.

In order to prevent intermediate positioning of the field member 26, the member 26 carries an operating arm 43 having a magnetic member 44 thereon. Opposing magnets 45 and 45' are mounted on suitable, fixed structure each adjacent one extreme of travel of the arm to attract and hold the arm in the extreme, fullthrow positions.

Alternatively, and as shown in dotted lines in FIG. 2, the arm 43 may be biased towards its extreme positions by other suitable means such as a coil spring 46 engaging the arm 43 and mounted in tension on a suitably adjacent fixed structure 47.

The two halves 38 and 39 of the field member 26 are formed of dissimilar materials to provide alternate modes of operation. The half 38 is formed of electrically conductive material, while the half 39 is formed of electrically non-conductive or insulating material. It is not imperative that the entire structure be so divided, but at least the surfaces 41 and 42 must be distinctly conductive and non-conductive, respectively.

The conductive half 38 is in electrical communication with a potential-controlling unit 49, such as a vari able generator shown, via a flexible line 48. The conductive roller 27 is similarly controlled by a potentialcontrolling unit 50. The potential controlling units include grounding terminals which are served by a common line.

In the position shown in solid lines in FIG. 2, the field formed between the non-conductive half 39 of the field member 26 and the conductive roller 27 is similar to the field shown in and described with reference to FIG. 1. The system is then operable to effect reverse development of latent charge images, as described hereinbefore. The member 26 is held securely in this position by magnetic attraction between the elements 44 and 45.

When direct development of latent charge images is desired, the operating arm 43 is movedover center and against the magnetic element 45, thereby presenting the conductive outer surface 41 of field-member half 38 to the back 22 of the paper sheet 21. In this configuration, the system is operable for development of latent images in the same manner and with the same advantages as the system disclosed in our copending US. application Ser. No. 277,059 filed Aug. 1, 1973.

Although the arcuate, pivoting field member 26 is preferred, it is to be understood that other arrangements may be used for selectively presenting conductive or non-conductive field-member surfaces to the back 22 of the strip.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter as described above or as shown on .the accompanying drawings is to be interpreted as illustrative and not as limiting.

What is claimed is:

1. Apparatus for uniformly developing a latent charged image carried on electrophotographic paper having an image side and a reverse side comprising:

a first field member including a main support surface;

a bath of charged liquid toner;

a second field member including a conductive roller partially immersed in said liquid toner bath and having a peripheral surface close to but spaced from said main support surface of said first field member;

transport means for moving the electrophotographic paper past said main support surface with the reverse side contacting said main support surface and the image side facing and spaced from said peripheral surface of said conductive roller;

drive means for rotating said conductive roller at a speed to form a thin layer of liquid toner on said peripheral surface of said conductive roller, said liquid toner forming a meniscus of liquid toner at the surface of the image side of the electrophotographic paper whereby liquid toner is uniformly distributed on the charged areas of the electrophotographic paper;

said main support surface of said first field member including a first conducting support surface and a second non-conducting support surface; and selecting means for selectively positioning one of said conducting and non-conducting support surfaces in position to support said electrophotographic paper.

2. The apparatus as recited in claim 1 including means for supplying predetermined electrical .potentials to said conductive roller.

3. The apparatus as recited in claim 2 including means for applying a predetermined potential to the conductive surface of said first field member.

4. The apparatus as recited in claim 1 wherein said main support surface has a convex configuration.

5. The apparatus as recited in claim 4 wherein said selecting means includes an axle on which said first field member is mounted, and means biasing said first field member away from an intermediate position of said main support surface.

6. The apparatus as recited in claim 5 wherein said biasing means includes a tension spring.

7. The apparatus as recited in claim 5 wherein said biasing means includes magnets. 

1. Apparatus for uniformly developing a latent charged image carried on electrophotographic paper having an image side and a reverse side comprising: a first field member including a main support surface; a bath of charged liquid toner; a second field member including a conductive roller partially immersed in said liquid toner bath and having a peripheral surface close to but spaced from said main support surface of said first field member; transport means for moving the electrophotographic paper past said main support surface with the reverse side contacting said main support surface and the image side facing and spaced from said peripheral surface of said conductive roller; drive means for rotating said conductive roller at a speed to form a thin layer of liquid toner on said peripheral surface of said conductive roller, said liquid toner forming a meniscus Of liquid toner at the surface of the image side of the electrophotographic paper whereby liquid toner is uniformly distributed on the charged areas of the electrophotographic paper; said main support surface of said first field member including a first conducting support surface and a second non-conducting support surface; and selecting means for selectively positioning one of said conducting and non-conducting support surfaces in position to support said electrophotographic paper.
 1. Apparatus for uniformly developing a latent charged image carried on electrophotographic paper having an image side and a reverse side comprising: a first field member including a main support surface; a bath of charged liquid toner; a second field member including a conductive roller partially immersed in said liquid toner bath and having a peripheral surface close to but spaced from said main support surface of said first field member; transport means for moving the electrophotographic paper past said main support surface with the reverse side contacting said main support surface and the image side facing and spaced from said peripheral surface of said conductive roller; drive means for rotating said conductive roller at a speed to form a thin layer of liquid toner on said peripheral surface of said conductive roller, said liquid toner forming a meniscus Of liquid toner at the surface of the image side of the electrophotographic paper whereby liquid toner is uniformly distributed on the charged areas of the electrophotographic paper; said main support surface of said first field member including a first conducting support surface and a second non-conducting support surface; and selecting means for selectively positioning one of said conducting and non-conducting support surfaces in position to support said electrophotographic paper.
 2. The apparatus as recited in claim 1 including means for supplying predetermined electrical potentials to said conductive roller.
 3. The apparatus as recited in claim 2 including means for applying a predetermined potential to the conductive surface of said first field member.
 4. The apparatus as recited in claim 1 wherein said main support surface has a convex configuration.
 5. The apparatus as recited in claim 4 wherein said selecting means includes an axle on which said first field member is mounted, and means biasing said first field member away from an intermediate position of said main support surface.
 6. The apparatus as recited in claim 5 wherein said biasing means includes a tension spring. 